The amount of dark matter produced during preheating is difficult to estimate analytically. The reason is that the parameters of the Whittaker–Hill equation evolve in time making the resonance stochastic,
which is further complicated by the non–trivial 3-D stability band structure [1]}.
Depending on the size of \(C_4\) , tangible backreaction and rescattering effects [2]},[3]} can also take place. Thus,
to make reliable predictions, we have to resort to lattice simulations.
